One of the things to take into consideration is that newer cameras with higher resolution sensors are going to place more demands on the lens quality needed for best results. IOW, they may not be capable of resolving enough line pairs/mm to take advantage of a denser sensor.

IOW, you may reach a point where you don't see any increase in detail captured with some lenses by going with a higher resolution sensor. I noticed that with a lot of the kit lenses that came out with 6MP cameras, where they started to show their limitations as higher resolution cameras came out. IOW, you could buy a 14MP versus 10MP camera and see little to no benefit to the higher resolution sensor with some lenses.

So, I suspect we'll see a lot of lenses upgraded as time passes, even though those lenses may have worked fine with the cameras (or film) available at the time they were first introduced.